Extraction, purification, and electrolytic precipitation of metallic zinc from smelter-fumes, zinc ores, and the like.



' 0. BEST.- EXTRACTION, .URIFICATION, AND ELECTROLYTIC PRECIPITATION 0F METALLIC ZINC FROM SMELTER FUMES, ZINC ORES, AND THE LIKE.

APPLICATION FILED SEPT. I6. 19H.

1,154, 01, Patntedfigyt. 28, 1915. a U I I I c IIIIII S;

WITNESSES mvEN op .w 1 '73- ATTORNEY UNITED STATES OFFICE.

OTTO BEST, OF SAN FRANCISCO, CALIFORNIIL.

EXTRACTION, PURIFICATION, AND ELECTROLYTIC PRECIPITATION 0F METALLICZINC FROM SMELTER-FUMES, ZINC ORES, AND THE LIKE.

Specification of Letters Patent.

Patented Sept. "8, 1915.

Application filed September 16, 1911. Serial No. 649,719.

To (171 whom it may concern I V Be it known that I, OTTO Bns'r, a citizen of the United States, residing at San Francisco,.in the-county of San Francisco and State of California, have invented new and useful In'iprovements in the Extraction-,-

' zinc. This I accomplishby roasting and leaching the same, purifying the salt obtained, precipitating,partly or entirely, the purified zinc salt in the form of hydroxid, carbonate,'and the like, (either unmixed. or mixed with an indifferent body like gypsum) by means'o'i' caustic alkali, alkali carbonate, alkaline earth, such as caustic soda,

- sodium carbonate, lime or magnesium oxid,

and .etlectrolyzing the salt, to obtain the zinc in a inetallic shape, while neutralizing the acid, whichis then, at the same time, freed by running it over the purified zinc hydroxid, carbonate or other zinc compound, insoluble in water, but soluble in weak acid and returning the liquor in a neutral or almost neutralcondition,'with practically the same saturation of zinc salts, and absolutely pure, to the electrolytic cell.

The successful electrolytic preparation of metallic zinc has been hampered in practice by the facts, that impure zinc salts, when electrolyzed, deposit the zinc in a spongy form,.that cannot be remelted. Again, the proper amount of free acid in solution and the proper control of the same has been found rather difiicult to obtain. Since these conditions are constantly changing, the current conditions. have to be changed, accordingly, which is another obstacle to the successful carrying out of this process.

In order to be a practical success, the

chemical extraction must be simple and fairly. complete, purification of the zinc salt practically complete, and chemical and electrical conditions in the cell must be as uniform as possible,'so that if the best conditions for depositing electrically a pure remeltable zinc are once established, they can bekept the same for weeks and months, when the same results must be obtained for a corresponding period.

In the drawing, the figure is a diagrammatic viewof an ap mratus for carrying out a part of my improved process' In the following described process, I have obtained .these ideal conditions, and have thus obtained'a pure zinc, not spongy, but capable of remelting. The zinc obtained in the laboratory from fumes has tested 99.2" and can easily be reinelted. I

The experiments were inainlycarried out with so called smelter fumes, which is a dust, collected in a bag'house provided for that purpose in some snielter's. It is a very refractory material, containing up to 30 and 35% metallic zinc. mainly in the form of zinc oxid and sulfate.fIt contains furthermore many kinds of products, partly valuable, partly valueless, such as silica, iron,

alumina, lime, magnesia, arsenic, antimony,

cadmium, lead, sulfur, sulfuric acid, organic matter, and others; furthermore silver and gold. The value of the latter two is largely depreciated through the presence of zinc, the terror of the smelter; the zinc on the other hand is difiicult to extract and to purify, on account 'of the many impurities present. Instead of smelter fumes, ore or other sources of zinc, with slight modifications, may be used.

I proceed in my process first chemically and then electrolytically, which are both part of one and the same process. The chemical part of theprocess is as follows: The fumes are first roasted at a low temperature, that is, made filterable and partially purified by the application of heat at a temperature below that of sulfatic roasting. The temperature is kept only high enough to char the organic matter and sublime the arsenic. In the presence of sulfates of a heavy metal, like iron or zinc sulfate, the arsenic sublimes readily, and practically completely. By this step, the most important of the chemical process, the following advantages are reached: (1) The material, that was, before roasting, difiicult to filter, is made filterable; (2) the organic is free of arsenic, while'the arsenic can be recovered at the same time; (4) the iron 1s oxidized and practically insoluble in weak acids and makes purification of the mother liquor easier andwhateyer traces of iron go ol s'ull ids oxidized tooxids and sulfates dissolved with some other salts.

and can be extracted by weak acid (tamper, for instance). The roasted material is now extracted with weak acid, for instance, sulit'uric, hydrochloric, or otl 1' suitable acid, in slight excess, and, it necessary, heated somewhat. Practically all the zincis easily In the laboratoryexperiments 9274. of the zinc and overwere extracted with sulfuric acid. All inunirit es can easily be removed by zinc oxid, and. a. little sodium sullid, used either successively or in one process, according to the products present and the object to be attained. The present process only relates", howcrer, to the solution, as this contains the zinc desired; The solution, as before stated, obtained from the roastedorc, is much purer than from the imroasted ore under otherwise the same conditions. This highly puritiedmotllcr liquor of zinc salts is now, precipitated in the form out hydroxid, carbonate, sullicl or other insoluble compound, that is insoluble in water, but soluble in weak acidsby means of a causticalkali, alkali sullid,.alk-ali car-initiate, alkaline earth like'caustic soda, sodiiiim sulticl, sodium can bonate, lime, magnesium, oxid and the like. For instance -1 rins ng-autos:

. I ziuorn, -ua,so,+au,o

(a znsorlua tezncoi afioi I now Wash these precipitates until all soluble impurities are removed and. lll'l'l ready for the next part of the process, that: of electrolysis.

The pure zinc salt solution placed in the electrolytic cell. 'Any suitable salt may be used "With any suitable density, at any suitable teinfgierature, with anv suitable elec' trmle, with or without a liaphragm. A. small amount olf pure sulfuric acid, best suited for electrolysis, is added to this solution. As "he Zi'uc salts used are pure, there quite a leeway, from a few huh dreilths of one per cent, of ld'per cent. and over, without danger of getting spongy zinc. Of course it is not advantageous, to go too high in free acid, as the loss oirgdi-xctricity is otherwise too high. 111.50 far as I am aware, it is broadly no lo use hnysalt, or-

ganic or inoro'ai'iuand, particilarly any zinc salt in tl Cnc way of :mcoumlishino as ltcllmviii:

any other suitable filter may be used.

ferring to the drawing, C indicates an electrolytic cell, which is filled with a zinc salt, preferably zinc sulfate. The same runs over into a storage tank S and contains zinc sulfate and some sulfuric acid. A pump 1. lifts it to two filtersVA', and A with false bottoms, filled, with zinc hydroxidgypsum mixture at such rate, as to get the desired acidity in the electrolytic cell. Of course In running the acid zinc sulfate solution through this layer of zinc hydroxid gypsum'mixturc, the free sulfuric acid is noutralizcd and at the same time zinc hydroxid is dissolved, leaving the gypsum behind, in soluble. The neutral-solution may pass an other filter, A,, holding zinc hydroxid gypsum mixture to get rid of the last trace of free sulfuric acid. and any possible mechanical and chemical impurities and be returned to the cell C at the bottom in a pure, neutral state. The aim, however, is to get the most suitable concentration of acid and zinc salt and otherwise the most suitable conditions, and to keep this concentration of acid and zinc salt and other conditions as much as possible the same.

By regulating the speed of the circulating liruor the desired amount of free acid in the cell is obtained. I can of course place the Wall, filter or dislike; I may press it into anode plates, alone or with insoluble or inditlerent materials.

The part of the electrolytic cycle of the process can of course be carried out with other metallic hydroxids like copper hydroxids made by the ammonia, or ammonia-eyanid or any other process, or any metallic hydroxids or water-insoluble com- -pound in a pure state, however obtained,

and leaching with a small. excess of sulfuric acid; substantially as described;

' 2. In the extraction of metallic zinc from zinc fumes, or the like, the preliminary step of obtaining a zinc salt suitable for forming the electrolyte which, comprises roasting the fumes in the presence of sul fates at a low temperature leaching with a small excess of sulfuric acid and purifying the solution thus obtained with zinc oxid and sodium sulficl; substantially as de-' scribed,

, 3. In the extraction of metallic zinc from zinc fumes, or the like, the preliminary step of obtaining a zinc salt suitable for forming the electrolyte which comprises roasting the fumes in the presence of sulfates at a low temperature and leaching with. a small excessof sulfuric acid, yurifying' the solution obtained with ;zinc oxal and sodium sulfid, and precipitating the pure zinc sulfate solution with lime to form zinc hydrate gypsum mixture; substantially as described.

4. Insthe extracti 11. of metallic zinc from zinc fumes, or the l ke, the preliminary step of obtaining a zinc salt suitable for forming the electrolyte which comprises roasting the fumesinthe presence of sulfates at a low temperature and leaching with a small excess of sulfuric acid, purifying the solution obtained With zinc oxid and sodium sulfid,

precipitating the pure zinc sulfate solution of sulfates at a low temperature and leach ing with a small excess of sulfuric acid,

purifying the solution obtained, precipitating the pure zinc sulfate solution with lime to form zinc hydrate gypsum mixture, wash ing said mixture with water to get rid of the soluble impurities, electrolyzing the pure zinc sulfate obtained and thereby depositing zinc on the cathode and forming sulfuric acid at the anode, pumping the acid zinc sulfate solution over the mixture of zinc hydrate and gypsum to neutralize the sulfuric acid, and returning the neutralized solution to the cell; substantially as described.

(3. In the extraction of zinc from zinc fumes or the like, the preliminary step of obtaining a solution appropriate for introduction into an electrolytic cycle, which comprises precipitating a metallic compound in a \Yater-insolublc form. easily s oluble in dilute acids, and introducing the same into the electrolytic cycle; substantially as described.

In testimony whereof I have hereunto set my hand in the presence of two subscribing witnesses.

OTTO BEST.

Witnesses:

Famous .lVmcrrr, D. BURICHARDS. 

